Method for charging gas into cassette pod

ABSTRACT

A method for transporting a cassette pod for containing semiconductor wafers is provided. The method includes transporting a cassette pod configured to receive a semiconductor wafer with a transporting apparatus. The method further includes supplying a gas from a cylinder into a housing of the cassette pod. The cylinder is externally positioned on the housing. The method also includes detecting a gas pressure in the cylinder with a detection element. In addition, the method includes issuing a signal to the transporting apparatus when the gas pressure in the cylinder is lower than a predetermined limit.

CROSS REFERENCE

This application is a Continuation of U.S. application Ser. No.15/825,192, filed on Nov. 29, 2017, now U.S. Pat. No. 10,475,683, whichis a Divisional of U.S. application Ser. No. 14/066,933, filed on Oct.30, 2013, now U.S. Pat. No. 9,837,293, issued on Dec. 5, 2017, theentirety of which are incorporated by reference herein.

BACKGROUND

In the manufacturing of a product, the product is usually processed atmany work stations or processing apparatus. A transporting of partiallyfinished products is therefore conducted in a manufacturing process.

For example, to complete the fabrication of semiconductor wafers,various steps of deposition, cleaning, ion implantation, etching andpassivation steps may be carried out before the semiconductor wafers arepackaged for shipment. Each of these fabrication steps may be performedin different process machines, i.e. a chemical vapor deposition tool, anion implantation tool, an etcher, etc. Therefore, the semiconductorwafers that are partially processed are transported between various workstations many times before the fabrication process is completed.

In some systems, cassette pods are used to store batches of thesemiconductor wafers. To conduct the transporting of the semiconductorwafers, the semiconductor wafers are moved into the cassette pods, andthe cassette pods and the semiconductor wafers are transported togetherby a handling and transport equipment. Operation of the handling andtransport equipment may be conducted under automatic control using aprogrammed computer which issues control signals for operating theequipment with little or no intervention by an operator. Therefore thehandling and transport equipment transports the cassette pods and thesemiconductor wafers between two positions for different purposes.

Consequently, a safe transporting of the semiconductor wafers in asemiconductor fabrication system is desired.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompany drawings.

FIG. 1 shows a schematic diagram of a semiconductor fabrication system,in accordance with some embodiments.

FIG. 2A shows a schematic diagram of a cassette pod, in accordance withsome embodiments.

FIG. 2B shows a cross-sectional view of a cassette pod, in accordancewith some embodiments.

FIG. 3 is a flow chart illustrating a method for charging a gas into acassette pod, in accordance with some embodiments.

FIG. 4 shows a schematic diagram of a semiconductor fabrication systemas a transportation apparatus is breakdown, in accordance with someembodiments.

FIG. 5 shows a schematic diagram of a semiconductor fabrication system,in accordance with some embodiments.

FIG. 6 shows a block diagram of the gas supply assembly, in accordancewith some embodiments.

FIG. 7 shows a cross-sectional view of a cassette pod, in accordancewith some embodiments.

FIG. 8 shows a cross-sectional view of a cassette pod, in accordancewith some embodiments.

FIG. 9 shows a cross-sectional view of a cassette pod, in accordancewith some embodiments.

FIG. 10 is a flow chart illustrating a method for charging a gas into acassette pod, in accordance with some embodiments.

DETAILED DESCRIPTION

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentscan be embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative, and do not limit thescope of the disclosure.

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the disclosure. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Moreover,the performance of a first process before a second process in thedescription that follows may include embodiments in which the secondprocess is performed immediately after the first process, and may alsoinclude embodiments in which additional processes may be performedbetween the first and second processes. Various features may bearbitrarily drawn in different scales for the sake of simplicity andclarity. Furthermore, the formation of a first feature over or on asecond feature in the description that follows include embodiments inwhich the first and second features are formed in direct contact, andmay also include embodiments in which additional features may be formedbetween the first and second features, such that the first and secondfeatures may not be in direct contact.

FIGS. 1-6 have been simplified for the sake of clarity to betterunderstand the embodiments of the present disclosure. Throughout thevarious views and illustrative embodiments, like reference numbers areused to designate like elements.

FIG. 1 shows a schematic diagram of a semiconductor fabrication system100 in accordance with some embodiments. The semiconductor fabricationsystem 100 is used in the semiconductor fabrication field. Thesemiconductor fabrication system 100 includes a processing apparatus110, a transporting apparatus 130, a stocker 150, and a number ofcassette pods 170. Additional features can be added to the semiconductorfabrication system 100, and some of the features described below can bereplaced or eliminated in other embodiments of the semiconductorfabrication system 100.

In accordance with some embodiments, the cassette pods 170 areconfigured for transporting a number of semiconductor wafers, e.g., 6wafers, 12 wafers, 24 wafers, etc. The cassette pods 170 may be asstandard mechanical interfaces (SMIFs) for loading semiconductor waferseach having a diameter of 200 mm (200 mm semiconductor wafers).Alternatively the cassette pods 170 may be front opening unified pods(FOUPs), which may be used to load 300 mm or 450 mm semiconductorwafers, or semiconductor wafers with larger diameter. Other types and/orsizes of wafer carrier or pod are, however, not excluded.

FIG. 2A shows a schematic diagram of one of the cassette pods 170, andFIG. 2B shows a cross-sectional view of one of the cassette pods 170, inaccordance with some embodiments. Each of the cassette pods 170 includesa housing 171 for containing a number of semiconductor wafers 120. Thehousing 171 includes a container 173 and a door 177, in accordance withsome embodiments. The container 173 may be opened when the door 177 isdisengaged to the container 173, as shown in FIG. 2A. Alternatively, thecontainer 173 may be closed when the door is engaged to the container173, as shown in FIG. 2B.

The container 173 has an upper wall 174, a lower wall 175, and a sidewall unit 176. The upper wall 174 is opposite to the lower wall 175. Theside wall unit 176 includes a numbers of side walls connected betweenthe upper wall 174 and the lower wall 175. In some embodiments, the sidewall unit 176 includes three side walls 1761, 1763, and 1765. The threeside walls 1761, 1763, and 1765 are consecutively connected between theupper wall 174 and the lower wall 175.

The door 177 is selectively engaged with the container 173. Thesemiconductor wafers 120 are loaded into the enclosure 172 of thecassette pod 170 or unloaded from the enclosure 172 of the cassette pod170 when the door 177 is disengaged from the container 173. When thedoor 177 is engaged to the container 173, the door 177 is held by theupper wall 174 and the lower wall 175, and the side walls 1761 and 1765,cooperatively. After the door 177 is engaged to the container 173, anenclosure 172 of the cassette pod 170 is formed inside of the housing171.

In some embodiments, each of the cassette pods 170 further includesmultiple supporting members 178 for supporting the semiconductor wafers120. The supporting members 178 are located inside of the enclosure 172,and the supporting members 178 are fixed at the side wall unit 176 ofthe container 173. In some embodiments, the supporting members 178respectively extend along a direction parallel to the upper wall 174 andthe lower wall 175. Therefore, the semiconductor wafers 120 supported bythe supporting members 178 is parallel to the upper wall 174 and thelower wall 175.

In some embodiments, each of the cassette pods 170 further includes agas inlet 179 enabling a gas to be charged into the enclosure 172. Insome embodiments, the gas inlet 179 is disposed on the lower wall 175,and the gas inlet 179 passes through the lower wall 175 and fluidlycommunicated with the enclosure 172. In some embodiments, each of thecassette pods 170 includes multiple gas inlets 179. For example, each ofthe cassette pods 170 includes four gas inlets 179 enabling a gas to becharged into the enclosure 172.

In some embodiments, each of the cassette pods 170 further includes aplate member 180. The plate member 180 is disposed on the upper wall 174of the housing 171. The plate member 180 is configured for being grippedby a gripper (not shown) of the transporting apparatus 130, as shown inFIG. 1.

Referring again to FIG. 1, the stocker 150 contains a number of meansfor holding and moving the cassette pods 170. For example, the stocker150 includes a number of rack portions 151 and a movement assembly 153.The cassette pods 170 are moved by the movement assembly 153 within thestocker 150 and are placed on the rack portions 151.

In some embodiments, the stocker 150 further includes a gas purgingassembly 155. The cassette pods 170 are moved into the gas purgingassembly 155 by the movement assembly 153 for charging a gas into theenclosures 171 of the cassette pods 170. In some embodiments, the gaspurging assembly 155 includes a purge tool 156. The purge tool 156 isfluidly connected to a gas source (not shown). The purge tool 156 hasone or more than one gas spreading member 1561. The number and the shapeof the gas spreading member 1561 may be varied depending on the numberand the shape of the gas inlet 179 of the cassette pods 170.

The transporting apparatus 130 is configured to transport or convey thecassette pods 170 to/from the stocker and/or the processing apparatus110. The transporting apparatus 130 includes a trail assembly 131, anoverhead hoist transport (OHT) assembly 133, and a transportingcontroller (not shown), in accordance with some embodiments. The trailassembly 131 is mounted on the ceiling of a FAB, for example. The OHTassembly 133 is suspended by the trail assembly 131, and thetransportation or the movement of the OHT assembly 133 on the trailassembly 131 is controlled by the transporting controller (not shown).

The OHT assembly 133 is equipped with a gripper (not shown) that cangrasp the cassette pods 170. The OHT assembly 133 transports thecassette pod 170 between the stocker 150 and the processing apparatus110. In some embodiments, the cassette pod 170 is transferred to theprocessing apparatus 110 from the stocker 150 by the followingoperations. First, the cassette pod 170 stored in the stocker 150 isgripped by the OHT assembly 133 and transferred along the trail assembly131 to the processing apparatus 110. When the OHT assembly 133 arrivesthe processing apparatus 110, the OHT assembly 133 is lowered down tothe processing apparatus 110, and the cassette pod 170 is placed on aload port 111 of the processing apparatus 110. Afterwards, the OHTassembly 133 is raised up to be transported by the trail assembly 131.

In some embodiments, the cassette pod 170 is removed from the processingapparatus 110 by the following operations. First, an empty OHT assembly133 is moved to the processing apparatus 110. Afterwards, the OHTassembly 133 is lowered down to the processing apparatus 110 to grip thecassette pod 170. Afterwards, the OHT assembly 133 with the cassette pod170 is hoisted and transferred to the stocker 150 along the trailassembly 131.

FIG. 3 is a flow chart illustrating a method 200 for charging a gas intothe cassette pod 170, in accordance with some embodiments. The method200 begins with an operation 201 in which semiconductor wafers (such asthe semiconductor wafers 120 as shown in FIG. 1), which have beenprocessed by a processing apparatus (such as the processing apparatus110 as shown in FIG. 1) are loaded into a cassette pod (such as thecassette pod 170 as shown in FIG. 2). After the semiconductor wafers 120are loaded into the cassette pod 170, the cassette pod 170 is closed.Such that, the semiconductor wafers 120 disposed in the cassette pod 170are protected from being contaminated.

The method 200 continues with an operation 203 in which the cassette pod170 is removed from the processing apparatus 110 to a gas purgingassembly (such as the gas purging assembly 155 as shown in FIG. 1) for agas purge processing. In some embodiments, the cassette pod 170 isremoved from the processing apparatus 110 by the transporting apparatus130. Afterwards, the cassette pod 170 is transported to the gas purgingassembly 155 disposed inside of the stocker 150, as shown in FIG. 1. Insome embodiments, the cassette pod 170 is removed from the processingapparatus 110 to a gas purging assembly disposed outside of the stocker150. In some embodiments, the gas charged into the cassette pod 170 isan inert gas, such as nitrogen gas or any other suitable inert gases.Nitrogen gas and/or other inert gases are used to prevent oxidation ofwafers during manufacturing.

The method 200 continues with an operation 205 in which the cassette pod170 is removed from the gas purging assembly 155 to be stored in thestocker 150. In some embodiments, the cassette pod 170 will not be movedout of the stocker 150 until another command is issued.

The method 200 continues with an operation 207 in which the cassette pod170 is removed from the stocker 150 to a processing apparatus. In someembodiments, the cassette pod 170 is removed from the stocker 150 to aprocessing apparatus other than the processing apparatus 110. In someembodiments, the cassette pod 170 is removed from the stocker 150 to theprocessing apparatus 110 again. In some embodiments, the cassette pod170 is removed from the stocker 150 to a stocker other than the stocker150.

In some embodiments, for each loading of the cassette pod 170 into thestocker 150 or unloading of the cassette pod 170 from the stocker 150takes 3-4 minutes. Also, the semiconductor fabrication system 100 isexpansive, for example, 50 meters in length. Transporting the cassettepod, especially cassette pod for carrying large size wafers such as 450mm, from a piece of the processing apparatus 110 to the stocker 150 mayalso take several minutes. Consequently, the operations mentioned aboveis time-consuming, and reduces an efficiency in manufacturingsemiconductor wafer.

Moreover, as shown in FIG. 4, in the period of transporting the cassettepod 170 from the processing apparatus 110 to the stocker 150, it ispossible that the cassette pod 170 cannot be transported to the stocker150 due to abnormal operations. For example, when breakdown of thetransporting apparatus 130 occurs, the transportation of thetransporting apparatus 130 is stopped, and the cassette pod 170 cannotbe transported to the stocker 150. Due to the delay of the schedule, thegas purging process cannot be executed to protect the semiconductorwafers 120 as plan. As a result, a damage of the semiconductor wafers120 may occur.

To reduce and/or resolve the problems mentioned above, a semiconductorfabrication system 100′ used in the semiconductor fabrication field isprovided, in accordance with some embodiments. As shown in FIG. 5, thesemiconductor fabrication system 100′ includes the processing apparatus110, the transporting apparatus 130, a processing apparatus 140, anumber of cassette pods 170′, and a processor apparatus 300.

In some embodiments, the processor apparatus 300 is configured forcontrolling operation of the processing apparatuses 110 and 140, thetransporting apparatus 130, and the cassette pods 170′. In some otherembodiments, the processor apparatus 300 is configured for monitoringthe processing apparatus 110 and 140, the transporting apparatus 130,and the cassette pods 170′. For the purpose of illustration, theprocessing apparatus 110 refers to the first processing apparatus, andthe processing apparatus 140 refers to the second processing apparatusin the following descriptions.

In some embodiments, the cassette pod 170′ is similar to the cassettepod 170 as shown in FIG. 2B. Differences between the cassette pod 170and the cassette pod 170′ include that the cassette pod 170′ furtherincludes a gas supply assembly 190 connected to the housing 171.

Referring to FIG. 6, a block diagram of the gas supply assembly 190 isillustrated, in accordance with some embodiments. The gas supplyassembly 190 includes a cylinder 191, a flow control valve 192, a flowcontroller 194, a detection element 196, and a tube 197, in accordancewith some embodiments.

The cylinder 191 may be made of a metal material such as iron, stainlesssteel, and/or aluminum. A pressurized gas is filled into the cylinder191 in advanced. The pressurized gas may be an inert gas, such asnitrogen gas.

The flow controller 194 is electrically connected to the flow controlvalve 192 to actuate the flow control valve 192. The flow control valve192, for example, is an electromagnetic valve and is fluidly connectedto the cylinder 191. After receiving an actuating signal from the flowcontroller 194, the flow control valve 192 is switched on, and the gasis discharged from the cylinder 191. After receiving another actuatingsignal from the flow controller 194, the flow control valve 192 isswitched off. Therefore, no gas is discharged from the cylinder 191. Insome embodiments, the flow control valve 192 is a proportionalelectromagnetic valve. The flow rate of the gas discharged from thecylinder 191 is controlled by the flow control valve 192.

In some embodiments, the detection module 196 is configured fordetecting the flow rate of the gas exhausted from the cylinder 191 (FIG.5) and transmitting a detection signal in accordance with the detectionresults to the processor apparatus 300 (FIG. 5). According to thedetection signals from the detection module 196, the processor apparatus300 determines whether or not to adjust the flow rate through a controlof the flow control valve 192.

In some embodiments, the detection module 196 is configured fordetecting gas pressure in the cylinder 191 (FIG. 5) and transmitting adetection signal in accordance with the detection results to theprocessor apparatus 300 (FIG. 5). Therefore, the processor apparatus 300is able to monitor the gas pressure in the cylinder 191 in real time.

In some embodiments, if the gas pressure in the cylinder 191 is lowerthan a predetermined limit, it means the gas in the cylinder is used up.Therefore, the cylinder 191 is replaced by another cylinder filled withinert gas. In some embodiments, when gas pressure in the cylinder 191 islower than a predetermined limit, the processor apparatus 300 issues arequest to transport the cassette pod 170′ (including the gas supplyassembly 190) to a work station (not shown), and the semiconductorwafers 120 are moved to another cassette pod 170′ which is equipped witha cylinder filled with inert gas.

As shown in FIG. 6, in some embodiments, the gas supply assembly 190further includes a wireless module 195. The gas supply assembly 190wirelessly communicates with the processor apparatus 300 (FIG. 5) viathe wireless module 195. The wireless module 195 is electricallyconnected to the flow controller 194 and the detection module 196. Insome embodiments, the wireless module 195 includes a radio-frequency(RF) signal receiver or infrared (IR) receiver to receive radio signals.In some embodiments, the wireless module 195 includes a radio-frequency(RF) signal transmitter or infrared (IR) transmitter for transmittingradio signals.

A control signal issued by the processor apparatus 300 (FIG. 5) istransmitted to the flow controller 194 via the wireless module 195. Adetection signal produced by the detection module 196 is radiated to theprocessor apparatus 300 via the wireless module 195. However, the gassupply assembly 190 may directly electrically connected to the processorapparatus 300 (FIG. 5) by other suitable means such as internet.

Referring to FIG. 7, a cross-sectional view of one of the cassette pods170′ is shown, in accordance with some embodiments. The gas inlet 179 isdisposed on the lower wall 175 of the housing 171. The tube 197 isfluidly connected between the flow control valve 192 and the gas inlet179. In some embodiments, one end of the tube 197 is fluidly connectedto the flow control valve 192 (FIG. 6), and the other end of the tube197 is fluidly connected to the gas inlet 179. Therefore, the gas flowa1 from the cylinder 191 flows through the flow control valve 192, thetube 197, and the gas inlet 179 and is charged into the enclosure 172,as shown in the arrows designated with reference number a1. Therefore,the semiconductor wafers 120 are surrounded by the gas flow a1 andprotected from being oxidized. However, it is appreciated that theposition of the gas inlet 179 can be varied according to demands.

For example, referring to FIG. 8, a cross-sectional view of one of thecassette pods 170″ is shown, in accordance with some embodiments. Thecassette pods 170″ differs from the cassette pods 170′ in that the gasinlet 179 is formed at the side wall unit 176 of the housing 171.Therefore, the gas flow a2 from the cylinder 191 flows through the flowcontrol valve 192, the tube 197, and the gas inlet 179 and is chargedinto the enclosure 172 from one side of the housing 171. The gas flow a2may be more steady and smooth as compared with the gas flow a1 incassette pods 170′, and the semiconductor wafers 120 are surrounded bythe gas flow a2 and protected from being oxidized.

Referring to FIG. 9, a cross-sectional view of one of the cassette pods170″′ is shown, in accordance with some embodiments. The cassette pods170″′ differs from the cassette pods 170′ in that the gas inlet 179 isformed at the upper wall 174 of the housing 171. Therefore, the gas flowa3 from the cylinder 191 flows through the flow control valve 192, thetube 197, and the gas inlet 179 and is charged into the enclosure 172from the top of the housing 171. The semiconductor wafers 120 aresurrounded by the gas flow a3 and protected from being oxidized.

Referring to FIG. 10, a flow chart illustrating a method 200′ forcharging a gas into the cassette pod 170′ is shown, in accordance withsome embodiments.

The method 200′ begins with an operation 211 in which semiconductorwafers (such as the semiconductor wafers 120 as shown in FIG. 5) whichhave been processed by a processing apparatus (such as the firstprocessing apparatus 110 as shown in FIG. 5) are loaded into a cassettepod (such as the cassette pod 170′ as shown in FIG. 5). After thesemiconductor wafers 120 are loaded into the cassette pod 170′, thecassette pod 170′ is closed. Such that, the semiconductor wafers 120,which are disposed in the cassette pod 170′, are protected from beingcontaminated.

The method 200′ also includes an operation 213 in which the cassette pod170′ is removed from the first processing apparatus 110 by thetransporting apparatus 130, and the cassette pod 170′ is moved to apredetermined destination. In some embodiments, the cassette pod 170′ isremoved from the first processing apparatus 110, and the cassette pod170′ is moved to a second processing apparatus (such as the secondprocessing apparatus 140 as shown in FIG. 5). After the cassette pod170′ is moved to a second processing apparatus, the semiconductor wafers120 are unloaded from the cassette pod 170′ orderly, and thesemiconductor wafers 120 are processed by the second processingapparatus 140. In some other embodiments, the cassette pod 170′ isremoved from the first processing apparatus 110 to a stocker, and thecassette pod 170′ is stored in the stocker.

The method 200′ further includes an operation 215 in which the enclosure172 of the cassette pod 170′ is charged with a gas from a gas supplyassembly (such as the gas supply assembly 190 as shown in FIG. 5)disposed on the housing 171 of the cassette pod 170′.

In some embodiments, the operation 215 is initiated no later than theoperation 213 is initiated. For example, the gas from the gas supplyassembly 190 is charged into the enclosure 172 before the cassette pod170′ is transported by the transportation apparatus 130.

In some embodiments, the operation 215 is finished prior to theoperation 213 is finished. For example, the operation 215 is finishedbefore the cassette pod 170′ is transported to the second processingapparatus 140. For another example, the operation 215 is finished beforethe cassette pod 170′ is transported to the stocker (not shown).

In some embodiments, the door 177 of the cassette pod 170′ (FIG. 7) isclosed immediately after the operation 211 is finished, and a request isissued by the processor apparatus 300 (FIG. 5) to initiate the operation215 simultaneously. In some other embodiments, a request is issued bythe processor apparatus 300 (FIG. 5) to initiate the operation 215before the door 177 of the cassette pod 170′ (FIG. 7) is completedclosed. Therefore, the semiconductor wafers 120 (FIG. 5) in the cassettepod 170′ can be protected by the gas from the gas supply assembly 190(FIG. 5) before the cassette pod 170′ is transported by thetransportation apparatus 130 (FIG. 5).

Embodiments of the disclosure have many advantages. For example, theoperation time for charging the gas into the housing of the cassette podis greatly reduced. Such a reduction of processing time also decreasescontamination and/or oxidization risk of the semiconductor wafers duringthe transportation of the cassette pod.

Embodiments of mechanisms for charging a gas into a cassette pod areprovided. A gas supply assembly is provided to be fluidly connected toan enclosure defined by a housing of the cassette pod. The gas can beprovided by the gas supply assembly during the transportation of thecassette pod between two different locations, or two differentprocessing apparatus, etc. Since it is not necessary to move thecassette pod into a gas purging assembly to implement a gas purgingprocess, the operation time is greatly reduced. Manufacturing efficiencyand production yield of the semiconductor wafers are greatly improved.

In accordance with some embodiments, a method for transporting acassette pod for containing semiconductor wafers is provided. The methodincludes transporting a cassette pod configured to receive asemiconductor wafer with a transporting apparatus. The method furtherincludes supplying a gas from a cylinder into a housing of the cassettepod. The cylinder is externally positioned on the housing. The methodalso includes detecting a gas pressure in the cylinder with a detectionelement. In addition, the method includes issuing a signal to thetransporting apparatus when the gas pressure in the cylinder is lowerthan a predetermined limit.

In accordance with some embodiments, a method for transporting acassette pod for containing semiconductor wafers is provided. The methodincludes processing a semiconductor wafer with a processing apparatus.The method further includes placing the semiconductor wafer processed bythe processing apparatus into a housing of a cassette pod. The methodalso includes supplying a gas from a cylinder into the housing, whereinthe cylinder is externally positioned on the housing. In addition, themethod includes detecting a gas pressure in the cylinder with adetection element. The method further includes moving the cassette podto a work station to replace the cylinder with another cylinder filledwith the gas in response to a signal issued by the detection element.The signal is issued when the gas pressure in the cylinder is lower thana predetermined limit.

In accordance with some embodiments, a method for transporting acassette pod for containing semiconductor wafers is provided. The methodincludes placing a housing of a cassette pod on a gas purging assembly.When the housing is placed on the gas purging assembly, a gas inlet ofthe housing is connected to a gas spreading member of the gas purgingassembly, and a gas is discharged from the gas purging assembly into thehousing via the gas spreading member and the gas inlet.

The method further includes removing the housing from the gas purgingassembly and mounting a cylinder to an outer surface of a side fixedwall of the housing. When the housing is removed from the gas purgingassembly, a tube is disposed outside of the housing and connects thecylinder to the gas inlet, and another gas is discharged from thecylinder into the housing via the tube and the gas inlet.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions, andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture,composition of matter, means, methods, and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. A method for transporting a cassette pod forcontaining semiconductor wafers, comprising: supplying a gas from acylinder into a housing of the cassette pod during transportation of thecassette pod by a transporting apparatus, wherein the cylinder isconnected to the housing; issuing a signal to the transporting apparatuswhen the gas pressure in the cylinder is lower than a predeterminedlimit; transporting the cassette pod to a work station when the signalis issued; and removing the semiconductor wafers to another cassette podwhich is equipped with another cylinder filled with the gas.
 2. Themethod as claimed in claim 1, further comprising: delivering the gasfrom the cylinder to the housing via a tube externally positioned on thehousing; and controlling a flow of the gas from the cylinder to thehousing with a flow control valve connected to the tube.
 3. The methodas claimed in claim 1, wherein the gas comprises nitrogen gas.
 4. Themethod as claimed in claim 1, further comprising processing thesemiconductor wafers with a processing apparatus; placing thesemiconductor wafers processed by the processing apparatus into thehousing of the cassette pod; and transporting the cassette pod from theprocessing apparatus to a predetermined destination with thetransporting apparatus.
 5. The method as claimed in claim 4, wherein thegas is supplied from the cylinder to the housing prior to removing thecassette pod from the processing apparatus.
 6. The method as claimed inclaim 4, wherein the gas is supplied from the cylinder to the housing nolater than removing the cassette pod from the processing apparatus. 7.The method as claimed in claim 4, wherein the predetermined destinationcomprises a stocker, and the method further comprises storing thecassette pod in the stocker.
 8. The method as claimed in claim 4,wherein the predetermined destination comprises another processingapparatus, and the method further comprises processing the semiconductorwafer with the another processing apparatus.
 9. The method as claimed inclaim 1, further comprising replacing the cylinder with another cylinderfilled with the gas when the signal is issued.
 10. The method as claimedin claim 4, further comprising: closing a door after the semiconductorwafers are loaded into the housing to form an enclosure and issuing arequest to initiate the charging of the gas simultaneously.
 11. A methodfor transporting a cassette pod for containing semiconductor wafers,comprising: processing the semiconductor wafers with a processingapparatus; placing the semiconductor wafers processed by the processingapparatus into a housing of the cassette pod; supplying a gas from acylinder into the housing of the cassette pod during transportation ofthe cassette pod by a transporting apparatus, wherein the cylinder isconnected to the housing, and the supply of the gas from the cylinder tothe housing is initiated prior to removing the cassette pod from theprocessing apparatus; moving the cassette pod to a work station toreplace the cylinder with another cylinder filled with the gas inresponse to a signal issued by a detection element when the gas pressurein the cylinder is lower than a predetermined limit; and transportingthe cassette pod with the transporting apparatus from the processingapparatus to a predetermined destination when the signal is not issued.12. The method as claimed in claim 11, further comprising: deliveringthe gas from the cylinder to the housing via a tube externallypositioned on the housing; and controlling a flow of the gas from thecylinder to the housing with a flow control valve connected to the tube.13. The method as claimed in claim 11, wherein the gas comprisesnitrogen gas.
 14. The method as claimed in claim 11, wherein the gas issupplied from the cylinder to the housing no later than removing thecassette pod from the processing apparatus.
 15. The method as claimed inclaim 14, further comprising: closing a door after the processedsemiconductor wafers are loaded into the housing to form an enclosureand issuing a request to initiate the supply of the gas simultaneously.16. A method for transporting a cassette pod for containingsemiconductor wafers, comprising: placing a housing of a cassette pod ona gas purging assembly including a purge tool; discharging a gas fromthe gas purging assembly into the housing via the purge tool; connectinga cylinder to the housing; and discharging another gas from the cylinderinto the housing after the cassette is removed from the gas purgingassembly.
 17. The method as claimed in claim 16, further comprising:transporting the cassette pod with a transporting apparatus while thegas is discharged from the cylinder into the housing; and detecting agas pressure in the cylinder with a detection element; wherein thetransporting apparatus moves the cassette pod to a work station toreplace the cylinder in response to a signal issued by the detectionelement when the gas pressure in the cylinder mounted on the housing islower than a predetermined limit.
 18. The method as claimed in claim 16,wherein the gas comprises nitrogen gas.
 19. The method as claimed inclaim 11, wherein the supply of the gas from the cylinder to the housingis finished before the cassette pod is transported to the predetermineddestination.
 20. The method as claimed in claim 11, wherein thepredetermined destination comprises another processing apparatus or astoker.